Research methods (1)

Question 1

How does conventional x-ray photography work?

Answer 1

An x-ray beam passes through an object, and different tissues absorb different amounts of radiation. The remaining (unabsorbed) radiation reaches a photographic plate to create an image.

Question 2

Why do x-rays work well for bones but not for the brain?

Answer 2

Because bones and flesh absorb x-rays very differently, creating high contrast — whereas brain tissues absorb x-rays similarly, producing almost no visible difference.

Question 3

What is the purpose of contrast x-ray techniques in brain imaging?

Answer 3

To enhance the visibility of specific brain areas by injecting a substance that absorbs x-rays differently than surrounding tissues, increasing image contrast.

Question 4

Why are contrast x-ray techniques useful for visualizing the brain?

Answer 4

Because brain tissues absorb x-rays similarly, and the injected contrast agent highlights certain areas (like blood vessels) that would otherwise be invisible.

Question 5

What is cerebral angiography?

Answer 5

A contrast x-ray technique that involves infusing a radio-opaque dye into a cerebral artery to visualize the cerebral circulatory system during x-ray imaging.

Question 6

What can cerebral angiograms detect?

Answer 6

• Vascular damage
• Blocked or ruptured vessels
• Displacement of vessels caused by tumors or swelling

Question 7

What is CT (computed tomography)?

Answer 7

A computer-assisted x-ray procedure that constructs 3D images of the brain by combining multiple cross-sectional x-rays taken from different angles.

Question 8

What is the process of a CT (Computed Tomography) scan?

Answer 8

The patient’s head is placed in a cylinder where an x-ray tube and detector rotate around it, taking multiple images at different levels. A computer combines these to create detailed, 3D brain images.

Question 9

What does PET (Positron Emission Tomography) measure and how does it work?

Answer 9

PET provides functional images of brain activity by measuring levels of radioactivity in different brain areas.

A radioactive substance fluorodeoxyglucose (FDG) similar to glucose is injected into the carotid artery. Active brain cells take it up but can’t metabolize it, so it accumulates in active areas.

Question 10

What does a PET scan show?

Answer 10

It shows a color-coded map of radioactivity levels across brain regions—indicating which areas were most active during a task.

Question 11

What is a key modern use of PET?

Answer 11

Identifying the distribution of neurotransmitters, receptors, or transporters using radioactively labeled ligands.

Question 12

What are the 3 main magnetic-field-based brain imaging techniques?

Answer 12

MRI, Diffusion Tensor MRI (DTI), and Functional MRI (fMRI)

Question 13

What is MRI?

Answer 13

MRI (Magnetic Resonance Imaging) is a structural brain imaging technique that produces high-resolution images using radio-frequency waves emitted by hydrogen atoms when they align with a powerful magnetic field.

Question 14

Why are hydrogen atoms used in MRI?

Answer 14

Because the body (and brain) contain lots of water (H₂O), and water contains two hydrogen atoms.

Different brain tissues have different amounts of water, so they produce different signals, allowing contrast between structures.

Question 15

How does MRI differ from CT scans?

Answer 15

• MRI uses magnetic fields and radio waves, not x-rays.
• MRI provides clearer, more detailed images (higher spatial resolution).
• MRI can create 3D images of the brain, unlike the slice-based CT images.

Question 16

What kind of information does MRI provide?

Answer 16

Structural information — it shows anatomy, tissue density, and abnormalities such as tumors, atrophy, or lesions.

Question 17

What is spatial resolution and how does MRI rank in it?

Answer 17

Spatial resolution = he ability to detect and represent differences in spatial location.
MRI has high spatial resolution, better than CT.

Question 18

What are the advantages and disadvantages of MRI?

Answer 18

Advantages of MRI?

• No radiation exposure
• Clear, detailed structural images
• Can visualize soft tissues and brain anatomy precisely

Disadvantages of MRI?
- Expensive
- Requires stillness (motion-sensitive)
- Unsafe for patients with metal implants or pacemakers

Question 19

What is Diffusion Tensor MRI (DTI)?

Answer 19

A method that maps the pathways of water diffusion in the brain, showing the major axon tracts (connections between brain regions).

Question 20

Why is DTI important in neuroscience?

Answer 20

It helps researchers study the connectome, or how brain structures are connected, which is crucial for understanding brain function.

Question 21

What is the Human Connectome Project?

Answer 21

A research project mapping all connections in the human brain to understand brain structure and function.

Question 22

What does functional MRI (fMRI) measure?

Answer 22

The BOLD signal (blood-oxygen-level-dependent signal), showing which brain areas receive more oxygenated blood during activity.

Question 23

Why does fMRI not measure electrical activity directly?

Answer 23

The BOLD signal reflects blood flow, not the neuronal action potentials, which happen much faster (milliseconds).

Question 24

Advantages of fMRI over PET scans?

Answer 24

1. No injection needed
2. Shows both structure and function in the same image
3. Better spatial resolution

Question 25

Limitations of fMRI?

Answer 25

1. Poor temporal resolution (BOLD takes 2–3 seconds; neural events occur in milliseconds) 2. BOLD signal only indirectly reflects neural activity

Question 26

What does oxygenated blood in active brain areas indicate in fMRI?

Answer 26

It accumulates in areas where neurons are active, allowing researchers to infer brain activity patterns during tasks.

Question 27

How does DTI complement fMRI?

Answer 27

DTI maps structural connections (tracts), while fMRI shows functional activity, together helping understand how brain areas communicate and function.